if you use outlook when you set up the account you'll see that when you set up a new email account there is a bax for "your name"
this is the from name, (put whatever you like in here). the username box is the name that's used to lo onto the server for authentication etc. (unless you set that differently in advanced options)

__________________
I didn’t fight my way to the top of the food chain to be a vegetarian…
Im sick of people saying 'dont waste paper'. If trees wanted to live, they'd all carry guns.
"The inherent vice of capitalism is the unequal sharing of blessings; The inherent vice of socialism is the equal sharing of miseries."

unfortunatly I don't have access to an excahnge server anymore since the place I work now uses IMAP mail due to greater flexibility.

but IIRC...

go to the users and computers pannel, and view the properties of the person you wish to change,
their display name should be on the same page as the rest of their details, including default mail address login name etc...

__________________
I didn’t fight my way to the top of the food chain to be a vegetarian…
Im sick of people saying 'dont waste paper'. If trees wanted to live, they'd all carry guns.
"The inherent vice of capitalism is the unequal sharing of blessings; The inherent vice of socialism is the equal sharing of miseries."

Going to Control Panel and users will only change users on the local machine.

Here are the steps to changing user email display name.

Go to... (on the exchange server)

Control Panel
Administrative Tools
Active Directory User and Computers
Right on the user you want to change
Click Properties
Change the display name in the "Display Name" field.
Click Ok

Wait about 15 minutes and see if the display name changes when they send email.

If not...

If I remember correctly...
Go to the user's properties again.
Click on the email address tab
If there is a CC address in the list...
Click on it and click edit and make sure the name matches the users new name.